The invention relates to double-edged cutting tips (inserts) for double-edged milling cutters equipped with only one single cutting tip. The cutting tip has a part-circular plate portion and a rear supporting face. Such a cutting tip is intended to be received in a transverse groove of a milling cutter body. The cutting tip is supported via its rear supporting face on a groove bottom of the transverse groove.
The cutting tip usually has a transverse bore in order to be able to attach the same to the milling cutter body by means of a mounting screw. Centering of the cutting tip within the milling cutter body can be effected either by means of the mounting screw or by means of a recess in the rear supporting face, which cooperates with a complementary projection in the region of the groove bottom of the transverse groove.
Such milling cutters are usually referred to as spherical milling cutters and are employed for copy milling. To this end, they should also be capable of "plunging-in or immersion", i.e. to perform milling also in axial direction of the milling cutter.
Such cutting tips usually have two spaced apart major faces which usually extend parallel to each other and preferably are plane-parallel. Furthermore, such cutting tips have oblique lateral faces, often referred to as flanks, which constitute an angle of less than 90.degree. with the respectively associated major face and whose lines of intersection with the respectively associated major face constitute a cutting edge each. So-called front or rake faces of the cutting edges are constituted by or in the major faces. The rake faces may have specific shape features, for example chip forming recesses, in order to obtain a desired chip shape.
The plane of the cutting tip through which the milling cutter axis extends when the cutting tip is inserted in the transverse groove of the milling cutter body is referred to as axial plane of the cutting tip in the context of present invention. That location on the periphery of the part-circular cutting tip portion through which the milling cutter axis extends when the cutting tip is inserted in the transverse groove of the milling cutter body, is referred to as cutting tip point or vertex.
On one side of the cutting tip vertex, there is formed a first cutting edge at the intersection between one major face and the lateral face located there, whereas on the other side of the cutting tip vertex, there is formed a second cutting edge at the intersection between the other major face and the associated part of the lateral face.
To enable the spherical milling cutter to penetrate the workpiece during milling, there are basically different forms of realization.
According to a first form of realization, each one of the parallel major faces also forms the rake face of the corresponding cutting edge. Each cutting edge is thus disposed above center, i.e. above the axial plane of the cutting tip as seen in cutting direction of the respectively associated cutting edge. Each cutting edge, in the region of the cutting tip vertex, thus has its own cutting edge point which is also located above center. To permit such a milling cutter to penetrate the workpiece, the two cutting edge points are connected by a transverse cutting line which constitutes an angle of more than 90.degree. with the axial plane of the cutting tip, as seen from the cutting edge of the respective major face towards the axial plane of the cutting tip. However, such a transverse cutting line has no cutting function but merely urges away the material to be milled. In the region of the milling cutter axis, the cutting speed of the cutting tip is thus zero and the milling cutter can only perform a pushing operation at this location. The longer the transverse cutting line is, the more pronounced cutting difficulties arise in the region of the cutting tip vertex. This problem can be reduced by reducing the length of the transverse cutting line. This can be achieved by forming recesses in both major faces in the region of the cutting tip vertex.
A second form of realization consists in lowering the rake face of each cutting edge with respect to the associated major face as far as the axial plane of the cutting tip. The two cutting edges are then both located in the axial plane of the cutting tip and constitute a common cutting edge point located on the milling cutter axis where the cutting speed is zero.
While a milling cutter having a cutting tip according to the latter realization is better capable of penetration during milling than milling cutters with a cutting tip according to the first-mentioned form of realization, there is, however, the disadvantage remaining that the cutting speed is zero at the cutting line tip or point. In case of a milling cutter having a cutting tip according to the latter form of realization, an additional disadvantage resides in that an inclination angle of zero is formed inevitably at the cutting edges located on the axial plane of the cutting tip. According to ISO standard, the inclination angle is understood to be the angle between the rake face or cutting edge and the axial plane of the milling cutter, i.e. the plane in which the cutting tip axial plane is located.
As is known, the disadvantage of an inclination angle of zero consists in that such a cutting edge geometry results in a jerk-like cutting operation, whereas cutting edges with an inclination angle other than zero (positive or negative, depending on the particular application) permit a smooth cutting operation.